The present invention relates to a control method of a compression ignition type engine and, more particularly, to a control method of optimizing ignition timing at a time of high torque at which a quantity of fuel has increased.
A conventional compression ignition engine is known, which is disclosed in JP A 10-252541 in which ignition is caused in the vicinity of a compression top dead center, avoiding a cold flame region which is caused before hot flame occurs.
However, in the conventional engine, a compression ratio is fixed. Compression ignition engines have a problem that combustion pressure increases rapidly and knocking occurs when torque is large (in the case where a fuel quantity is large and an air fuel ratio is small). This is because auto-ignition occurs earlier than a suitable ignition time and flame has been propagated from that portion as a fire source. In this manner, since the conventional compression ignition engine has not a forcible igniting means such as a spark ignition device, there is a problem that ignition timing at a time of high torque can not be controlled.
An object of the present invention is to enable timing of compression ignition to be controllable.
In order to achieve the above object, in the present invention, a cylinder-inside state (temperature or pressure) inside an engine combustion chamber after compression is estimated or detected before occurrence of a combustion phenomenon, and a quantity of EGR and timing of intake/exhaust valve opening/closing are controlled so that the cylinder-inside state enters a cold flame region which becomes a trigger of compression ignition phenomenon.
Concretely, there are provided a valve mechanism including an intake valve and an exhaust valve each incorporated with an engine cylinder, a fuel injection valve having an injection port opened inside a combustion chamber surrounded by a piston and a cylinder wall of the engine, operation state detecting means for detecting operation states of the engine, air fuel ratio setting means for setting air fuel ratios, cylinder-inside state estimating means for estimating temperature or pressure inside the cylinder and cylinder-inside state controlling means for controlling temperature or pressure inside the cylinder, and the cylinder-inside state controlling means controls so that the cylinder-inside temperature or pressure in the vicinity of the compression top dead center passes through a cold flame region which is an ignition range of fuel expressed by relations of temperature and pressure, based on the estimation results estimated by the cylinder-inside state estimating means.
Further, concretely, in the present invention, there is the following feature. That is, when the nature of gasoline (for example, regular gasoline or high octane gasoline) is determined, a limit of ignition by compression is determined in a relation between a cylinder-inside pressure (which changes depending on the position of a piston) and a temperature of a gaseous mixture (refer to FIG. 4B and FIG. 8). In a region 43 of a prescribed temperature and pressure state, pre-combustion (cold flame) which does not directly influence on torque generation occurs. In the present invention, an air fuel ratio is controlled so that the cold flame is generated prior to combustion (hot flame) which directly influence on torque generation.
It is a matter of course that it is possible to generate the cold flame prior to combustion (hot flame) which directly influences on torque generation by controlling cylinder-inside pressure or cylinder-inside temperature under the condition that an air fuel ratio is fixed to a prescribed value.
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